Numerous clinical reports describe the recurrence of solid tumors and leukemias in patients years after successful treatment of the primary neoplasm. These reports suggest that small numbers of tumor cells persist in a dormant state in patients during periods of prolonged clinical remission. Thus, the tumor dormant state is defined as one in which viable tumor cells persist in a clinically normal host for prolonged periods of time. To date, few studies have directly addressed themselves to the problem of tumor dormancy. Therefore, little is known of the host tumor cell interaction that results in the establishment and maintenance of the tumor dormant state. The broad scope of our research project is an understanding of all host-tumor cell interactions that are involved in establishment and maintenance of the tumor dormant state established in DBA/2 mice by sinecomitant immunization and challenge with L5178Y cells. The objectives of this proposal are to determine whether endogenous viruses and the immune responses to them play an important role in the establishment and maintenance of the tumor dormant state established in DBA/2 mice by sinecomitant immunization with L5178Y lymphoma cells. We will first determine in vitro whether immune responses to endogenous viruses are present in tumor dormant mice, then determine whether they are operative in vivo, and finally attempt to prolong the tumor dormant state by stimulating immune responses to the virus antigens.